1. Field of the Invention
The present invention relates to a liquid jet apparatus for ejecting liquid drops of a plurality of kinks different in volume from the same nozzle opening and a method for driving the same.
2. Description of the Related Art
An ink jet recorder which is an example of a liquid jet apparatus has a recording head having many nozzle openings formed in a row, a carriage mechanism for moving the recording head in the main scanning direction (the width direction of recording paper), and a paper feed mechanism for moving a recording paper in the sub-scanning direction (the paper feeding direction).
The recording head has a plurality of pressure chambers each interconnected to each of the nozzle openings and a plurality of pressure generation elements each for changing the ink pressure in each of the pressure chambers. In the recording head, a driving pulse is fed to the pressure generation element, thereby the ink pressure in the pressure chamber is changed, and then, an ink drop is ejected from the nozzle opening.
The carriage mechanism moves the recording head in the main scanning direction. During this movement, the recording head ejects ink drops in the timing specified dot pattern data. When the recording head reaches the terminal of the movement range, the paper feed mechanism moves the recording paper in the sub-scanning direction. When the movement of the recording paper is finished, the carriage mechanism moves the recording head in the main scanning direction again and the recording head ejects ink drops during movement.
By performing the aforementioned operation repeatedly, an image on the basis of the dot pattern data is recorded on the recording paper.
The recorder records an image depending on whether or not to eject ink drops, that is, existence of dots. Therefore, in this recorder, a method for representing the intermediate gradation by representing one pixel by a plurality of dots such as 4xc3x974 and 8xc3x978 is adopted. To record a high-quality image by this method, it is necessary to eject ink drops with an extremely small volume from the recording head.
With the foregoing in view, to satisfy conflicting requests of improvement of the image quality and improvement of the recording speed, an art for ejecting ink drops different in size from the same nozzle is proposed. For example, by supplying a plurality of pulse signals capable of generating minute ink drops, a plurality of minute ink drops are ejected from the same nozzle, and the respective ink drops are joined before reaching on the recording paper, and a large ink drop is generated.
However, in this art, the number of ink drops to be joined before reaching on the recording paper is limited, so that the size of ink drops is limited and the variable range of size is narrowed. Furthermore, since a plurality of ink drops must be joined before reaching on the recording paper, the control is inevitably difficult.
Therefore, an art for generating a driving signal connecting a plurality of kinds of driving pulses in series depending on the volume of ink drops to be ejected and supplying a driving pulse obtained from this driving signal to the pressure generation element can be considered.
However, in the aforementioned art, when a plurality of kinds of driving pulses are connected simply in series, the driving period (the period of the driving signal) necessary to record one dot becomes inevitably longer. Namely, in this art, it is necessary to connect driving pulses in correspondence to the number of the kinds of ink volumes to be ejected and the driving period becomes longer in correspondence to the number of connected driving pulses. And, when the driving period becomes longer, the recording speed becomes slower.
Further, at the nozzle openings of the recording head, the meniscus, that is, the free surface of ink exposed at the nozzle openings is exposed to the air, so that an ink solvent (for example, water) evaporates gradually. When the ink viscosity of ink at the nozzle openings rises due to evaporation of the ink solvent, a fault such as a splash of ejected ink drops in a direction shifted from the normal direction may be caused.
Therefore, in the ink jet recorder, ink is stirred by minute vibration of the meniscus and an increase in ink viscosity at the nozzle openings is prevented. At the time of stirring by the minute vibration, a minute vibration pulse is applied to the pressure generation element so as to cause a pressure change in the pressure chamber and the meniscus is slightly moved or vibrated in the ejection and pull-in directions.
However, when driving pulses for ejecting ink drops from the nozzle openings and a minute vibration pulse for generating minute vibration in the meniscus are simply connected in series so as to form the aforementioned driving signal, the time of one driving period becomes longer and the printing speed is reduced.
The present invention was developed with the foregoing in view and is intended to efficiently put a plurality of driving pulses for ejecting a plurality of kinds of ink drops different in ink volume and a minute vibration pulse for causing minute vibration to the meniscus in a driving signal of one driving period.
To solve the aforementioned problems, a liquid jet apparatus according to the present invention comprises: a pressure generation element installed in correspondence to a pressure chamber interconnected to a nozzle opening, said pressure generation element adapted to be applied with a driving pulse thereby causing a pressure change to a liquid in said pressure chamber to eject a liquid drop from said nozzle opening; driving signal generation unit to generate a driving signal to be used for generating a plurality of kinds of said driving pulses for ejecting said liquid drop and a minute vibration pulse to be applied to said pressure generation element so as to finely vibrate a meniscus of said liquid; and pulse generation unit to generate said minute vibration pulse and said driving pulses by selecting a part of said driving signal, wherein said driving signal includes a plurality of waveform elements to be used to generate a plurality of kinds of said driving pulses and a connection element connecting said waveform elements between different voltage levels and not to be used to generate said driving pulses, and wherein said pulse generation means generates said minute vibration pulse by a combination of at least a part of said waveform elements and at least a part of said connection element.
Preferably, said driving pulses eject a plurality of kinds of said liquid drops different in volume, said driving pulse for ejecting said liquid drop of a smallest volume being generated by a combination of a plurality of said waveform elements, and said minute vibration pulse is generated by a combination of a part of a plurality of said waveform elements for ejecting said liquid drop of a smallest volume and at least a part of said connection element for connecting said part of a plurality of said waveform elements for ejecting said liquid drop of a smallest volume to another said waveform element.
Preferably, a part of said waveform elements for ejecting said liquid drop of a smallest volume is formed in a step shape, said connection element for connecting said part of a plurality of said waveform elements for ejecting said liquid drop of a smallest volume to another said waveform element is formed in a step shape, and
said minute vibration pulse is generated by a combination of a half of said waveform element of a step shape and a half of said connection element of a step shape.
Preferably, said connection element follows said part of a plurality of said waveform elements for ejecting said liquid drop of a smallest volume, and said connection element expands or contracts said pressure chamber in the same direction as said part of a plurality of said waveform elements for ejecting said liquid drop of a smallest volume does and then contracts or expands said pressure chamber in the opposite direction.
Preferably, said part of a plurality of said waveform elements used for generating said minute vibration pulse is a preparatory waveform element which contracts said pressure chamber of waiting condition without ejecting said liquid drop.
Preferably, a single pulse of said minute vibration pulse is generated in a single period of said driving signal.
Preferably, said minute vibration pulse is generated from said at least a part of said waveform elements and said at least a part of said connection element following said at least a part of said waveform elements.
Preferably, said plurality of waveform elements include ejection waveform elements for operating said pressure generation element so as to eject said liquid drops from said nozzle opening and charging waveform elements for operating said pressure generation element so as to charge said pressure chamber with said liquid, and said pulse generation means generates said plurality of kinds of said driving pulses depending on timing for selecting said ejection waveform elements and said charging waveform elements.
Preferably, said plurality of kinds of said driving pulses eject a plurality of kinds of said liquid drops different in volume, and said plurality of waveform elements include a pair of said ejection waveform elements for ejecting said liquid drop of a largest volume and said ejection waveform element, disposed between said pair of said ejection waveform elements, for ejecting said liquid drop of a smallest volume.
Preferably, said pressure generation element comprises a piezo-electric vibrator of a deflection vibration mode.
Preferably, said pressure generation element comprises a piezo-electric vibrator of a longitudinal vibration mode.
To solve the aforementioned problems, a method according to the present invention for driving a liquid jet apparatus with a pressure generation element installed in correspondence to a pressure chamber interconnected to a nozzle opening, said pressure generation element adapted to be applied with a driving pulse thereby causing a pressure change to a liquid in said pressure chamber to eject a liquid drop from said nozzle opening, comprises the steps of: generating a driving signal to be used for generating a plurality of kinds of said driving pulses for ejecting said liquid drop and a minute vibration pulse to be applied to said pressure generation element so as to finely vibrate a meniscus of said liquid; and
generating one of said minute vibration pulse and said driving pulses by selecting a part of said driving signal, wherein said driving signal includes a plurality of waveform elements to be used to generate a plurality of kinds of said driving pulses and a connection element connecting said waveform elements between different voltage levels and not to be used to generate said driving pulses, and wherein said minute vibration pulse is generated by a combination of at least a part of said waveform elements and at least a part of said connection element.
Preferably, said driving pulses eject a plurality of kinds of said liquid drops different in volume, said driving pulse for ejecting said liquid drop of a smallest volume being generated by a combination of a plurality of said waveform elements, and said minute vibration pulse is generated by a combination of a part of a plurality of said waveform elements for ejecting said liquid drop of a smallest volume and at least a part of said connection element for connecting said part of a plurality of said waveform elements for ejecting said liquid drop of a smallest volume to another said waveform element.
Preferably, a part of said waveform elements for ejecting said liquid drop of a smallest volume is formed in a step shape, said connection element for connecting said part of a plurality of said waveform elements for ejecting said liquid drop of a smallest volume to another said waveform element is formed in a step shape, and said minute vibration pulse is generated by a combination of a half of said waveform element of a step shape and a half of said connection element of a step shape.
Preferably, said connection element follows said part of a plurality of said waveform elements for ejecting said liquid drop of a smallest volume, and said connection element expands or contracts said pressure chamber in the same direction as said part of a plurality of waveform elements for ejecting said liquid drop of a smallest volume does and then contracts or expands said pressure chamber in the opposite direction.
Preferably, said part of a plurality of said waveform elements used for generating said minute vibration pulse is a preparatory waveform element which contracts said pressure chamber of waiting condition without ejecting said liquid drop.
Preferably, a single pulse of said minute vibration pulse is generated in a single period of said driving signal.
Preferably, said minute vibration pulse is generated from said at least a part of said waveform elements and said at least a part of said connection element following said at least a part of said waveform elements.
Preferably, said plurality of waveform elements include ejection waveform elements for operating said pressure generation element so as to eject said liquid drops from said nozzle opening and charging waveform elements for operating said pressure generation element so as to charge said pressure chamber with said liquid, and said pulse generation means generates said plurality of kinds of said driving pulses depending on timing for selecting said ejection waveform element and said charging waveform element.
Preferably, said plurality of kinds of said driving pulses eject a plurality of kinds of said liquid drops different in volume, and said plurality of waveform elements include a pair of said ejection waveform elements for ejecting said liquid drop in a largest volume and said ejection waveform element, disposed between said pair of said ejection waveform elements, for ejecting said liquid drop of a smallest volume.
Preferably, said pressure generation element comprises a piezo-electric vibrator of a deflection vibration mode.
Preferably, said pressure generation element comprises a piezo-electric vibrator of a longitudinal vibration mode.
The present invention will be understood more fully from the detailed description given hereunder and from the accompanying drawings of the preferred embodiments of the invention. However, the drawings are not intended to imply limitations of the invention to a specific embodiment, but are for explanations and understandings only.